Most of today's commercially available personal watercraft have a hull and a deck disposed directly thereon. The deck has a pedestal onto which a straddle-type seat is disposed. When such watercraft travel over waves, the forces due to impacts between the hull and the waves are transferred to the driver and passengers which can make the riding experience uncomfortable, especially over long distances. The only cushioning against these impacts is provided by the padding in the seat.
In an effort to minimize the transfer of these forces to the driver and passengers, some watercraft have a suspension element, such as a spring and damper assembly, disposed between the seat and the deck. Although this reduces the transfers of these forces to the body of the driver and passengers, this arrangement tends to still solicit the legs of the driver and passengers since the seat now moves relative to the footrests formed in the deck as well as, for the driver, the hands and arms that have to follow the movement of the helm assembly.
Another way to minimize the transfer of these forces to the driver and passengers consists in suspending the whole deck above the hull. The engine, fuel tank, and propulsion system are still in and/or connected to the hull and a sub-deck is disposed on the hull to protect the components in the hull from water. The hull and sub-deck together form a hull and sub-deck assembly (HSD) assembly. The deck is suspended on the HSD assembly. In this arrangement, the footrest can still be formed with the deck, and as such the legs of the drivers and passengers are less solicited than in watercraft where only the seat is suspended.
One problem when designing a personal watercraft having a suspended deck is that the weight of the driver, passengers, and/or cargo will have a large impact on the performance of the suspension.
In other vehicles such as cars or motorcycles, the majority of the weight of the vehicle is suspended. In a motorcycle for example, the frame, engine, fuel tank, and seat, to name a few, are all suspended on the wheels of the motorcycle. Since the suspended mass is relatively large, the mass of the driver, the presence or absence of passengers and/or cargo has little effect. This is because the mass of an additional passenger is only a small percentage of the suspended mass of the motorcycle. This percentage is even smaller for a car. As such, the suspensions for these vehicles can be designed for one suspended mass (suspended mass of vehicle plus an estimated mass to take into account loading of the vehicle) and will operate adequately regardless of the mass of the driver, the presence or absence of passengers and/or cargo.
In watercraft where the deck is suspended, a fair amount of the mass is not suspended since the heavier components are in the hull. The deck itself is fairly light in comparison. Thus the amount of load on the deck has a significant effect. The presence of a driver, passengers, and cargo can triple the mass suspended on the HSD assembly, if not more. This means that the suspension needs to accommodate these larger variations. Using a spring that is having a low spring rate will cause the suspension to operate adequately when only a driver is present on the deck, but may cause the deck to impact the HSD assembly when passengers and cargo are also on the deck. Using a spring having a high spring rate will cause the deck to operate adequately when a driver, passenger, and cargo are on the deck, but will be too stiff when only a driver is present, thus not absorbing the forces being transferred to the HSD assembly as effectively.
Therefore, there is a need for a personal watercraft having a suspension that can operate adequately over a wide range of load on the deck.
Also, personal watercraft can be used in different conditions. These can vary from the high waves of the ocean to the relatively flat water of a lake. In the first example a stiffer suspension would be preferred, however in the second example a softer suspension would be preferred to better absorb the forces. Different drivers may also want different riding experiences. Some may want to feel the waves while others may want a more stable and comfortable ride.
Therefore, there is also a need for a personal watercraft having a suspension that can accommodate different riding conditions and/or driver preferences.